Previously we have shown significant changes in pulmonary functional measurements in adolescent asthmatics with exercise induced bronchospasm following inhalation of either 1.0 ppm or 0.5 ppm of sulfur dioxide (SO2) plus a sodium chloride (NaCl) droplet aerosol during 10 minutes exercise on a treadmill. During the coming year, we plan to investigate the acute effects of exposure to 100 ug/m3 of sulfuric acid (H2SO4) in similar asthmatic subjects. All exposures will be at greater or less than 75% relative humidity (RH) and 22 degrees C. Exposures will be carried out for 30 minutes at rest followed by 10 minutes of moderate exercise on a treadmill. The pulmonary functional parameters measured will be: a) total respiratory resistance (RT); b) functional residual capacity (FRC); c) maximal flow (Vmax50 and Vmax75); d) forced expiratory volume in one second (FEV1). We also plan to recruit a group of atopic adolescents who do not have extrinsic asthma or exercise-induced bronchospasm. This group was chosen because it should represent those atopic adolescents with the lowest risk of airways hypersensitivity. This group will be exposed to the following three exposure modes: a) 1mg/m3 NaCl droplet aerosol; b) 0.5 ppm of SO2 plus 1 mg/m3 NaCl droplet aerosol; c) 1.0 ppm of SO2 plus 1 mg/m3 NaCl droplet aerosol. The exposure and recording protocol will be the same as described above.